Development of Polymer Systems with High Electron Mobility for Photovoltaic Applications

Dr. Frank W. Harris and Dr. Stephen Z. D. Cheng, UA, in collaboration with Dr. Michael Durstock, AFRL

Dr. Frank W. Harris

The University of Akron

Department of Polymer Science

Akron, OH  44325-3909

Voice:  (330) 972-5459

Fax:  (330) 972-5704

Email:  fharris@uakron.edu

Web Page:  Dr. Frank W. Harris

Project Description

New electron-deficient polymers and discotic liquid crystals are being synthesized, characterized and evaluated as electron-acceptors in photovoltaic applications.  The work is focused on the utilization of nitrogen-containing heterocyclic structures such as pyridinium salts and quinoxalines.  Quinoxalines have previously been identified as good conductors for n-type photovoltaic materials.  Pyridinium salts have also been shown to be extremely electron-deficient molecules undergoing facile one-electron reductions to form radical cations.  These systems are being used along with MDMO-PPV in the design and construction of photovoltaic devices, which are being evaluated at Wright-Patterson Materials Laboratory.  Device models are also being constructed and used to improve device design and efficiency.

Accomplishments

A series of poly(pyridinium salts) (PPSs), a series of poly(phenylquinoxalines) (PPQs) and a series of quinoxaline-containing discotic molecules (Fig. 1) have been synthesized.  The PPSs and the PPQs have been used with MDMO-PPV in the construction of photovoltaic devices.  Although both systems displayed low power conversion efficiencies, the PPQ devices displayed excellent open circuit voltages.  To understand these results, the donor polymer (MDMO-PPV), was modeled using existing theoretical frameworks in order to understand the efficiency problems present in the described acceptor systems.  The results of the model correlate very well with existing device data, and have helped to produce a targeted approach to future acceptor syntheses.  Preliminary characterization and evaluation of the discotic liquid-crystalline quinoxalines indicate that they have considerable promise as electron conductors.

Group Members in Collaboration

Dr. Dong Zhang (Post-doctoral Research Associate)

Mr. Jie Hu (graduate student)

Mr. Andrew Soehnlen (graduate student)

Mr. Jeremy Warren (graduate student)

Figure 1.  Chemical Structure of the New Electron-deficient Discotic Molecules.